A common method for installing electrical wiring in residential, commercial and other structures, involves the placement of electrical wiring into electro-metallic tubing (EMT), otherwise commonly referred to as conduit. Conduit is rigid, hollow, bendable, thin-walled metal tubing, that is used to interconnect metal electrical boxes placed throughout the structure, forming a network used to convey electricity. Flexible conduit as well as plastic conduit and electrical boxes are also commercially available. Conduit is connected to itself and electrical boxes using a variety of specialized connectors and hardware, together forming a continuous pathway into which electrical wiring is placed for routing to all desired locations.
Conduit is widely used in electrical wiring applications. Two major benefits to the use of conduit for electrical wiring are safety and convenience. Since wires are completely enclosed within the conduit/electrical box network, electrical fires or other wiring related problems can be contained. From the standpoint of convenience, the conduit/electric box network provides a permanent, continuous pathway for routing electrical wiring to all locations, even in enclosed and inaccessible areas. Wiring may be introduced into or removed from conduit at any time, as electrical needs change or maintenance is required.
Conduit is manufactured in several tubing diameters, with ½ and ¾ inch diameters being typical and widely used. The choice of diameter to be used is made based on the quantity or size of wires to be installed. Within the overall network of conduit and electrical boxes, individual segments or lengths of conduit can vary considerably, based on the distance between electrical box connections. Lengths of conduit segments can range from a few feet up to 50 feet or more depending on requirements. Over shorter distances, depending on the quantity of wires to be installed, wires may simply be installed by pushing them into and through the conduit by hand. Greater distances, a larger quantity of wires, or other circumstances require equipment, instead of simply pushing, in order to move the wires through the conduit from one location to another. This may be due to any of several factors including lack of stiffness or rigidity exhibited by the wire(s), multiple bends in the conduit that may be encountered, and the overall resistance within the conduit due to friction.
The piece of equipment commonly used to install wires in conduit is called a fish tape. In its simplest Form the fish tape consists of a flexible, flattened, stiff steel wire (50 feet long is common), coiled into a reel-like housing which restrains it to prevent unintentional unwinding. The fish tape is payed out of and wound into the housing, by passing it through a slot that is slightly narrower than the width of the wire, creating an interference fit to prevent unintentional unwinding. The fish tape is introduced into and moved back and forth through the conduit to facilitate placement of wires. The tip of the fish tape is formed into a blunt, hook-like or eyelet shape, to ease its forward movement when pushed into and through the conduit away from the operator, and to facilitate attachment of wires for pulling them into and through the conduit toward the operator.
In normal use, the blunt, hook-like tip of the fish tape is introduced through the open front of an electrical box, and into the open end of a conduit segment where it is connected to the electrical box. The operator continues to withdraw the fish tape in short sections from within the fish tape housing, incrementally pushing it into the conduit, and advancing it gradually toward the opening at the opposite end of the conduit segment. This process continues until the necessary distance is traveled, and the hook-like tip of the fish tape emerges at the opposite end of the conduit segment and into the electrical box.
The operator then attaches the desired wires to the hook-like tip, so they may be pulled back into and through the conduit segment toward the electrical box at which the tip of the fish tape was originally inserted. The operator continues to pull the fish tape and attached wires back through the conduit a few feet at a time, incrementally rewinding the fish tape back into its housing. This process continues until the necessary distance is traveled, and the tip of the fish tape and wires emerge at the electrical box where originally inserted.
The fish tape and its method of use have several disadvantages as follows:
(1) The process of paying out and rewinding the fish tape into the fish tape housing is labor intensive and requires continuous, repeated motions by the operator. Continuous repeated motion operations have been associated with health care problems such as carpal tunnel syndrome.
(2) The fish tape can only be moved through a conduit segment in short increments, resulting in significant labor time spent installing wires in each conduit segment. On an overall project basis, labor cost for a specific work objective may be high, or less work accomplished in a given amount of time.
(3) The blunt, hook-like shape of the fish tape tip often makes it difficult to move through the conduit due to snagging on connections or other irregularities within the conduit segment. The fish tape may become stuck in the conduit segment, and may even be broken during a forceful retrieval attempt.
(4) Long conduit segments, especially those with many bends and direction changes, increase friction on and resistance to fish tape movement. This, combined with potential snagging or sticking within the conduit segment, can significantly add to the time and effort required, and affect job cost and efficiency.
(5) The fish tape, being itself a flattened metal wire, will conduct electricity, and could represent an electrical shock hazard to the operator or others under certain conditions.
Various attempts have been made to provide a vacuum system for installing wiring in conduits as described in U.S. Pat. Nos. 5,334,000, and including components for use in such systems as set forth in D246,823 and D312,336. To date, none of those systems has met with widespread commercial acceptance due to the cumbersome nature of their designs. The present disclosure addresses these problems.